Generally, to insert a catheter into a blood vessel, the vessel is identified by aspiration with a long hollow needle in accordance with the well-known Seldinger technique. In its simplest application, a needle, with a syringe attached, is introduced into the patient. When blood enters the syringe, it provides visual indication that the vessel has been found; the syringe is then disconnected from the needle and a thin guidewire is then introduced into the needle and into the interior of the vessel. The introducer needle is then removed from the patient and slid over the guidewire proximal end, leaving the distal end portion of the guidewire that has been inserted into the vessel within the vessel and the opposing end of the guidewire projecting beyond the surface of the skin of the patient. After which, the catheter is directed over the guidewire, either directly or using a dilator or the like.
During the procedure, when the syringe is removed from the introducer needle, bleeding can occur from the needle and onto the operative field, or air can be aspirated into the vessel if the patient inspires while the needle is not sealed prior to and during introduction of the guidewire into the needle. Blood on the operative field exposes the caregivers to contamination with blood-borne pathogens, and intravascular air can result in vascular occlusion and injury or death. Currently this is controlled by the interventionist by putting their finger tip on the needle hub.